This circuit is for traditional old-style telephone lines found in an American 1980s documentation. Components are common and the optical coupler can be replaced with an equivalent.
In fact, the 556 consists of a double 555, which can be replaced by these integrated ones. The...
This is the basic version of a small audio oscillator with the LM3909. The circuit must be powered...
This oscillator controlled based on a CMOS 4011 can produce signals from a few hertz up to more...